1. Field of the Invention
The invention relates in general to a light source module for collecting reflective beam from light source, and more particularly to a light source module for collecting reflective beam from light source applicable in a projection display system.
2. Description of the Related Art
Currently, either the liquid crystal display (LCD) technology, or digital light processor (DLP) technology (generally having one or three micro-mirror devices (DMD)) are commonly employed in the projection display system (projector).
FIG. 1 illustrates a schematic of a conventional projection display system using LCD as an imager. The projection display system 100 comprises a lamp 105, a reflector 110, a polarizer 115, the LCDs 120, 125 and 130, the separating dichroics 140, 145 and 150, the combining dichroics 160, 165 and 170, and a projection lens 180.
The lamp 105, such as metal halide bulb, tungsten halogen lamp or other arc discharge lamp, is coupled to the reflector 110. The reflector 110 focuses the light produced by the lamp 105 and turns it into an incident beam 107. The incident beam 107 passes through the reflective polarizer 115 (or polarizing beam splitter, PBS), which is an essential element to separate two orthogonally polarized light beams, and is separated into the lights of color red (R), green (G) and blue (B) by the separating dichroics 140, 145 and 150, respectively.
In the projection display system 100 of FIG. 1, three liquid crystal displays (LCDs) 120, 125 and 130 are used as the electro-optical light modulation panels (also known as imagers or light valves) for color red (R), green (G) and blue (B). The red (R), green (G) and blue (B) homogeneous light then pass through the LCDs 120, 125 and 130, and impinge on the combining dichroics 160, 165 and 170, respectively. Finally, composite light consisting of the red, green and blue homogeneous light impinges on a projection lens 180, and is magnified and projected on the screen 190. The liquid crystal display has individually addressable cells, which become individually controllable picture elements or pixels in the display environment.
Although the projection display system 100 described above comprises three LCDs, it is possible to have a projection display system comprising only one light modulation panel (one LCD-panel or one DMD-panel), monochrome or color. The image projection theories of both are similar. A projection display system comprising only one light modulation panel, for example, has a light source (comprising a lamp and a reflector) to produce an incident beam to enter a surface of a polarizer. The polarizer allows the incident light with particular polarization to exit from the other surface of the polarizer. Then, the incident light with particular polarization passes through the light modulation panel having red (R), green (G) and blue (B) filters, and impinges on a projection lens. The image is consequently magnified and projected on the screen.
FIG. 2 illustrates a schematic of another conventional projection display system using digital micro-mirror device (DMD) as an imager. The projection display system 200 comprises a lamp 205, a reflector 210, a color wheel 215 and a digital micro-mirror device (DMD) 220.
The lamp 205 coupled to the reflector 210 illuminates the light. The reflector 210 focuses the light and turns it into an incident beam 207. The color wheel 215 functions similarly as the PBS, separating the incident beam 207 into the lights of color red (R), green (G) and blue (B). Please also refer to FIG. 2B, which is a front view of the color wheel of FIG. 2A. The color wheel 215 is a spinning red/green/blue color sequential disc producing millions of colors in the projected image. When the incident beam 207 impinges the red regions 2151 of the color wheel 215, the red light is allowed to pass through the color wheel 215 and reaches the DMD 220. But the green and blue lights are reflected by the red regions 2151 and cannot pass through the color wheel 215. Similarly, if the incident beam 207 impinges the green regions 2152 of the color wheel 215, only green light is allowed to pass through the color wheel 215, and the red and blue lights are reflected by the green regions 2152. The blue regions 2153 of the color wheel 215 only allow the blue light of three colors to pass through.
In the projection display system 200 of FIG. 2, a digital micro-mirror device (DMD) 220 is used as the imager. The digital micro-mirror device (DMD) 220, also known as the Deformable Mirror Device, comprises numerous mirrors (not shown). Each mirror corresponds to a particular pixel of in the projected image and operates in a binary manner where each mirror cell switches between “ON” and “OFF”. After the red (R), green (G) and blue (B) lights sequentially pass through the color wheel 215, the mirror deflection of the DMD 220 creates a full color image on the screen 290.
One problem with the projection display system 100 in FIG. 1 is that only the incident light with particular polarization is allowed to pass through the reflective polarizer 115, the other incident light without particular polarization is reflected and turns in a reflective beam 109. Reflection typically accounts for a loss of 50% of the incident beam 107. The projection display system 200 in FIG. 2 also has the problem of light inefficiency. Since only one of three colors can pass through the color wheel 215 at a time, the other two colors will be reflected and turns into the reflective beam 209; thus, reflection typically accounts for a loss of two-third of the incident beam 207.
Therefore, the conventional projection display systems 100 and 200 suffer from the considerable loss of light. For example, the loss of the projection display system 100 having LCD-imager is about 50%, and the projection display system 200 having DMD-imager is 66%. Such the disadvantage will cause the low light efficiency for projection display system.